Working or machining of the contact faces of rails is often necessary. In this sense, substantially two types of applications may be involved, namely:
improvement of the surface quality in new rails, for example for high-speed routes, where the rolled quality is not sufficient; and PA1 reprofiling used rails.
The contact surfaces of used rails have two defects resulting from plastic deformation, namely deformation of the cross section of the contact surface and the development of ridges in the longitudinal direction.
Both defects increase the driving resistance of the route, and the ridges play an important role. They appear together with cracks and have a self-inducing effect, which once the ridges have developed can lead to rail breakage within a relatively short time.
Various chip-removing techniques, such as planing, grinding and milling, are used for machining the contact surfaces.
Planing typically involves high costs for plant and tools; it also has an unfavorable effect in terms of machining, namely the production of continuous chips, which build up edges and thus negatively affect the surface quality.
With grinding, an equivalent surface quality is attainable, but for process-dictated reasons, only slight machining depths can be attained. Especially when such used rails are machined, this presents problems in terms of the time expended when the machining must be performed at least to the depth of the cracks. Test results indicate that eliminating the ridges by removal of material down to the depth of the lower flanks leads to the reappearance of the ridges after a short period of use. It is therefore desirable for the reprofiling to be performed at least to the depth of the cracks. The depths involved are up to 2 mm, and because of the order of magnitude of the machining volume, milling can be considered a highly suitable method. In the earlier known apparatus, profile millers arranged with vertical or horizontal shafts were used, which generate the profile either with a plurality of tangentially arranged tracks or with profile cutters. In both cases, tool costs are high, and imprecision in dimensions or positioning of the individual cutters often causes problems in the quality and profile accuracy of the worked surface.